1. Field of the Invention
This invention relates to the detection of chemicals, and particularly to a device for detecting the presence of specific chemical materials, more especially, but not exclusively, gases, amongst a plurality of chemical materials.
2. Description of Related Art
Although there have long been in existence devices, such as pellistors, which can detect the presence of a specific material, such a device cannot detect individually, with the same high sensitivity, a number of such materials.
More recently, devices have been proposed which use an array of sensors, each of which is primarily sensitive to a particular chemical material. The primary material is different for each sensor, but the sensors have overlapping broadband selectivity characteristics, so that each sensor responds differently from the others to all of the materials under test. Each sensor provides electrical outputs corresponding, respectively, to each of the materials. Corresponding outputs of all of the sensors are fed to information processing means, which determines from the signals provided by the corresponding outputs a "feature vector" which represents the material. From a comparison of this feature vector with such vectors of known substances the particular material is identified. Similar information processing is effected for each of the sets of corresponding outputs from the sensors, enabling identification of the other materials within the operating range of the sensors.
In such known devices the information processing is effected on the basis of the responses of the detectors once they have reached a state in which their outputs are steady, but a number of different materials may give rise to the same sensor responses.